The present invention relates to inkjet printheads. In particular, it relates to an arrangement of a bubble chamber having a curved or convex wall portion partially surrounding a rectangular heater element.
The art of inkjet printing is relatively well known. In general, an image is produced by emitting ink drops from a printhead at precise moments such that they impact a print medium at a desired location. The printhead is supported by a movable print carriage within a device, such as an inkjet printer, and is caused to reciprocate relative to an advancing print medium and emit ink drops at times pursuant to commands of a microprocessor or other controller. The timing of the ink drop emissions corresponds to a pattern of pixels of the image being printed. Other than printers, familiar devices incorporating inkjet technology include fax machines, all-in-ones, photo printers, and graphics plotters, to name a few.
A conventional thermal inkjet printhead includes access to a local or remote supply of color or mono ink, a heater chip, a barrier layer, a nozzle or orifice plate attached or formed with the heater chip, and an input/output connector, such as a tape automated bond (TAB) circuit, for electrically connecting the heater chip to the printer during use. The heater chip, in turn, typically includes a plurality of thin film resistors or heater elements fabricated by deposition, masking and etching techniques on a substrate such as silicon.
To print or emit a single drop of ink, an individual heater is uniquely addressed with a predetermined amount of current to rapidly heat a small volume of ink. This causes the ink to vaporize in a local bubble chamber (between the heater and nozzle plate) and to be ejected through the nozzle plate towards the print medium. The shape of the ink chamber often conforms to the shape and orientation of its attendant heater.
Problematically, when both the heater and bubble chamber have rectangular shapes, stagnant regions can develop in the bubble chamber and serve to trap air bubbles in the ink. Over time, trapped bubbles accumulate and grow large enough to prevent proper heat transfer. Eventually, the heaters fail or have lessened functionality.
Accordingly, a need exists to prevent air bubble formation and accumulation in inkjet printheads.
The above-mentioned and other problems become solved by applying the principles and teachings associated with the hereinafter described printhead having a curved wall bubble chamber.
In one embodiment, the invention teaches an inkjet printhead with a substantially rectangular heater element. By dividing a length by a width dimension, the heater element has an aspect ratio of more than about 2.0. More preferably, it has an aspect ratio of about 4.0 or 5.0 or greater than about 2.5. A bubble chamber with a curved or convex wall portion partially surrounds the heater element. A radius of an arc of the curved wall portion is greater than the width dimension of the heater element while less than the length dimension and none of the curved wall portion overlies a periphery of the heater element. In other embodiments, the radius is greater than one-half the width dimension while less than one-half the length dimension and none of the convex wall portion overlies a periphery of the heater element. An ink ejection side of an orifice, which exists through a thickness of a nozzle plate covering the bubble chamber, resides directly above the heater element. Preferred length and width dimensions include about 35 and 13 microns or 40 and 10 microns with a radius of about 16 microns. The bubble chamber may be formed in the nozzle plate, in a plurality of layers defining the heater chip or in a barrier layer between the nozzle plate and the heater chip.
In other aspects of the invention, the bubble chamber includes a rectangular wall portion connected to the convex wall portion and either portion may occupy a terminal end of the bubble chamber. Comer regions of the rectangular portion may include chamber cuts, fillet cuts or other.
In either bubble chamber embodiment, an ink flow channel through one of the bubble chamber walls has a primary direction of ink flow substantially paralleling a length dimension of the heater element. Two substantially parallel ink flow walls define the primary direction and are oriented substantially parallel to the length dimension and substantially perpendicular to a longitudinal extent of an ink via. Similar to the bubble chamber, the ink flow channel may be formed in the nozzle plate, in a plurality of layers defining the heater chip or in a barrier layer between the nozzle plate and the heater chip.
Inkjet printers for housing the printheads are also disclosed.
These and other embodiments, aspects, advantages, and features of the present invention will be set forth in the description which follows, and in part will become apparent to those of ordinary skill in the art by reference to the following description of the invention and referenced drawings or by practice of the invention. The aspects, advantages, and features of the invention are realized and attained by means of the instrumentalities, procedures, and combinations particularly pointed out in the appended claims.